Deck 9: Hemoglobin: an Allosteric Protein

Question 1

The form of hemoglobin found in the R state is called _____________.

Answer 1

oxyhemoglobin

Question 2

In normal adult hemoglobin, HbA, the β6 position is a glutamate residue, whereas in sickle-cell hemoglobin, HbS, it is a(n) _____________ residue.

Answer 2

valine

Question 3

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: The substance produced when carbon dioxide reacts with water.

Answer 3

l

Question 4

Carbon dioxide reacts with the amino-terminal groups of hemoglobin to form carbamate groups, which carry a(n) _____________ charge.

Question 5

The T state of hemoglobin is stabilized by a salt bridge between β1 Asp 94 and the C-terminal _____________ of the β1 chain.

Question 6

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: This iron atom in heme is bound to the fifth coordination site of the molecule.

Question 7

2,3-bisphosphoglycerate binds only to the _____________ form of hemoglobin.

Question 8

The binding of 2,3-bisphosphoglycerate to hemoglobin _____________ (increases, decreases) its affinity of oxygen binding.

Question 9

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: This is the chemical form in which most of the carbon dioxide is transported in the blood.

Question 10

The effect of pH on oxygen binding of hemoglobin is referred to as the _____________.

Question 11

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: The type of binding that is indicated by a sigmoidal-shaped binding curve.

Question 12

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: The type of hemoglobin that is composed of two α chains and two γ chains.

Question 13

As the partial pressure of carbon dioxide increases, the affinity of oxygen binding to hemoglobin _____________.

Question 14

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: This condition is a result of a single point mutation in the β chain of hemoglobin.

Question 15

Under normal conditions, the heme iron in myoglobin and hemoglobin is in the _____________ oxidation state.

Question 16

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: The molecule whose function is to facilitate diffusion of oxygen in muscle cells.

Question 17

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: The shape of the myoglobin binding curve that shows that it is not regulated allosterically.

Question 18

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: This method of studying hemoglobin monitors changes in magnetic fields during the binding of oxygen.

Question 19

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) cooperative
b) oxygen
c) fMRI
d) carbamate
e) histidine
f) hyperbolic
g) myoglobin
h) bicarbonate ion
i) sickle-cell anemia
j) protoporphyrin
k) fetal
l) carbonic acid
____________: The organic portion of the heme group in hemoglobin.

Question 20

The ability of myoglobin to bind oxygen depends on the presence of a bound prosthetic group called _____________.

Question 21

Which of the following is correct concerning the oxygenation plot of proteins X and Y, shown below?

A) Protein Y exhibits tighter oxygen binding than does protein X.
B) Protein Y corresponds to fetal hemoglobin; protein X corresponds to normal adult hemoglobin.
C) Protein X corresponds to fetal hemoglobin; protein Y corresponds to normal adult hemoglobin.
D) Protein X corresponds to myoglobin; protein Y corresponds to hemoglobin.
E) None of the above.

Question 22

What factor(s) influence(s) the binding of oxygen to myoglobin?

A) the concentration of bicarbonate ion, HCO3−
B) the partial pressure of oxygen, pO2
C) the concentration of hemoglobin present
D) the concentration of 2,3-BPG
E) B and D

Question 23

What is fetal hemoglobin? How does it differ from adult hemoglobin?

Question 24

Which of the following describes the Bohr effect?

A) Lowering the pH results in the release of O2 from oxyhemoglobin.
B) Increasing the pressure of CO2 results in the release of O2 from oxyhemoglobin.
C) Increasing the pH increases the T form of hemoglobin.
D) All of the above.
E) A and B.

Question 25

Describe the octahedral coordination sphere of the iron ion in hemoglobin and myoglobin.

Question 26

Which of the following statements is correct for hemoglobin and oxygen transport?

A) The oxygen binds to the proximal histidine residue of the globin chain.
B) Bonding of carbon dioxide to hemoglobin molecules increases the binding of oxygen.
C) Hemoglobin binds more oxygen as the pH is lowered.
D) Hemoglobin binds more oxygen at higher BPG concentrations.
E) The binding of each O2 molecule to hemoglobin increases its affinity for the next O2 molecule.

Question 27

Which of the following is not correct concerning myoglobin?

A) The globin chain contains an extensive α-helix structure.
B) The heme group is bound to the globin chain by two disulfide bonds to cysteine residues.
C) The iron of the heme group is in the Fe+2 oxidation state.
D) The diameter of the iron ion decreases upon binding to oxygen.
E) The function of myoglobin is oxygen storage in muscle.

Question 28

The structure of normal adult hemoglobin can be described as:

A) a tetramer composed of four myoglobin molecules.
B) a tetramer composed of two αβ dimers.
C) a tetramer composed of two α2 and two β2 dimers.
D) a tetramer composed of two α2 and two γ2 dimers.
E) None of these accurately describe hemoglobin.

Question 29

Which statement is most correct?

A) Curve X most likely corresponds to pH 7.2.
B) Curve Z most likely corresponds to pH 7.6.
C) Hb has a higher affinity for oxygen at the pH of curve Z.
D) Curve Y most likely corresponds to pH 7.4.
E) pH has no effect on the oxygenation of hemoglobin.

Question 30

What is the Bohr effect?

A) the ability of hemoglobin to retain oxygen when in competition with myoglobin
B) the regulation of hemoglobin binding by hydrogen ions and carbon dioxide
C) the alteration of hemoglobin conformation during low-oxygen stress
D) All of the above.
E) None of the above.

Question 31

Sickle-cell anemia is caused by:

A) a decreased production of α chains of hemoglobin.
B) a substitution of a glutamic acid residue for a phenylalanine residue at the β6 position.
C) the loss of the heme group because the proximal His is oxidized.
D) a substitution of a valine residue for a glutamic acid residue at the β6 position.
E) a substitution of glutamic acid residue for histidine at the C terminal of the α chain.

Question 32

Which of the following is not correct concerning the oxygenation plot of proteins X and Y, shown below?

A) Protein X exhibits tighter oxygen binding than protein Y.
B) Protein Y would function as a better transport protein than protein X.
C) Protein X exhibits cooperative binding; Y does not.
D) Protein X corresponds to myoglobin; protein Y corresponds to hemoglobin.
E) Protein Y contains multiple binding sites.

Question 33

What functional role does the distal histidine play in the function of myoglobin and hemoglobin?

Question 34

Hemoglobin binding of oxygen is best described as a:

A) concerted model.
B) Michaelis-Menten model.
C) sequential model.
D) combination of sequential and concerted models.
E) None of the above.

Question 35

Which of the following is correct concerning fetal hemoglobin?

A) Fetal hemoglobin is composed of two α and two γ subunits.
B) Fetal hemoglobin binds 2,3-BPG more tightly than normal adult hemoglobin.
C) Fetal hemoglobin binds oxygen less than HbA at all pO2.
D) Fetal hemoglobin does not exist in the T form.
E) None of the above.

Question 36

Why is it advantageous for hemoglobin to have allosteric properties?

Question 37

Which of the following is correct concerning the differences between hemoglobin and myoglobin?

A) Both hemoglobin and myoglobin are tetrameric proteins.
B) Hemoglobin exhibits a hyperbolic O2 saturation curve, while myoglobin exhibits a sigmoid-shaped curve.
C) Hemoglobin exhibits cooperative binding of O2, while myoglobin does not.
D) Hemoglobin exhibits a higher degree of O2 saturation at all physiologically relevant partial pressures of O2 than does myoglobin.
E) All of the above.

Question 38

Carbon dioxide forms carbamate groups in proteins by reaction with:

A) aspartate residues.
B) cysteine residues.
C) N-terminal amino groups.
D) tyrosine residues.
E) heme groups.

Question 39

Which of the following is correct concerning the following equilibria? CO2 + H2OH2CO3

A) An increase in the pressure of CO2 will result in a decrease of pH.
B) This reaction is catalyzed by carbonic anhydrase.
C) The H2CO3 dissociates to H+ and bicarbonate ion, HCO3−.
D) The majority of CO2 is transported to the lungs in the form of HCO3−.
E) All of the above.

Question 40

What would be the expected result of a lysine residue being substituted with a serine residue in the BPG binding site of hemoglobin?

A) BPG would bind more tightly because of the loss of a positive charge.
B) BPG would bind more tightly because of the gain of a positive charge.
C) BPG would bind less tightly because of the loss of a positive charge.
D) BPG would bind less tightly because of the gain of a positive charge.
E) This substitution would have no effect on the binding of BPG.

Question 41

Briefly describe the cause of sickle-cell anemia.

Question 42

Describe the chemical basis of the Bohr effect.

Question 43

Briefly describe cooperative binding.

Question 44

Describe the role of 2,3-bisphosphoglycerate in the function of hemoglobin.

Question 45

Use the concerted model to explain allosteric cooperative binding.

Question 46

Describe how carbon dioxide affects the oxygenation of hemoglobin.

Question 47

Describe the structure of normal adult hemoglobin.